Abstract
AbstractA better understanding of regional‐scale precipitation patterns in the Himalayan region is required to increase our knowledge of the impacts of climate change on downstream water availability. This study examines the impact of four cloud microphysical schemes (Thompson, Morrison, Weather Research and Forecasting (WRF) single‐moment 5‐class, and WRF double‐moment 6‐class) on summer monsoon precipitation in the Langtang Valley in the central Nepalese Himalayas, as simulated by the WRF model at 1 km grid spacing for a 10 day period in July 2012. The model results are evaluated through a comparison with surface precipitation and radiation measurements made at two observation sites. Additional understanding is gained from a detailed examination of the microphysical characteristics simulated by each scheme, which are compared with measurements using a spaceborne radar/lidar cloud product. Also examined are the roles of large‐ and small‐scale forcings. In general, the schemes are able to capture the timing of surface precipitation better than the actual amounts in the Langtang Valley, which are predominately underestimated, with the Morrison scheme showing the best agreement with the measured values. The schemes all show a large positive bias in incoming radiation. Analysis of the radar/lidar cloud product and hydrometeors from each of the schemes suggests that “cold‐rain” processes are a key precipitation formation mechanism, which is also well represented by the Morrison scheme. As well as microphysical structure, both large‐scale and localized forcings are also important for determining surface precipitation.
Highlights
The mountainous Himalayan region, often called the “water tower” of Asia, is the source of many major rivers, providing water for hundreds of millions of people living downstream [Viviroli et al, 2007]
This study examines the impact of four cloud microphysical schemes (Thompson, Morrison, Weather Research and Forecasting (WRF) single-moment 5-class, and WRF double-moment 6-class) on summer monsoon precipitation in the Langtang Valley in the central Nepalese Himalayas, as simulated by the WRF model at 1 km grid spacing for a 10 day period in July 2012
The schemes are able to capture the timing of surface precipitation better than the actual amounts in the Langtang Valley, which are predominately underestimated, with the Morrison scheme showing the best agreement with the measured values
Summary
The mountainous Himalayan region, often called the “water tower” of Asia, is the source of many major rivers, providing water for hundreds of millions of people living downstream [Viviroli et al, 2007]. It is understood that the topography of the Himalayan region has a profound impact on the spatial distribution of precipitation [e.g., Anders et al, 2006; Bookhagen and Burbank, 2006, 2010; Das et al, 2006], which can show large variations on scales of 1-10 km, patterns of precipitation are poorly constrained as in situ rain gauge measurements are insufficiently dense and unevenly distributed They are situated predominately on valley floors and away from the highest areas of precipitation, which exist on the mountain slopes and tops [Steinegger et al, 1993; Winiger et al, 2005; Anders et al, 2006; Immerzeel et al, 2015]
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